The phrase comes from Disco Inferno, the 1976 disco hit by The Trammps, where burn baby burn is the song's driving chorus hook and a call to keep dancing as the floor heats up. It later reached a wider audience through the Saturday Night Fever era, when disco anthems became shorthand for high-energy celebration. Clipped down to just the shout, it now circulates online as a quick reaction sound, because the line already carries its own meaning: something is hot, intense or about to go too far.